At a certain stage in the process of manufacturing glass lamp bulbs, for example, incandescent lamps connected to hollow glass tubes projecting like stems, also called "stem lamps", the interiors of the lamps are brought, by so-called pumping and vacuum machines, into a condition which is dependent upon the intended use of the lamp. In the case where the interior must be evacuated, the stem lamps are connected to a vacuum source. Thereafter, the stems are melted or otherwise sealed off. If the interior must be filled with a particular gas, it is subjected to a pumping-sweeping cycle and subsequently filled with gas under a predetermined pressure before the stem is melted off or sealed off.
The pumping machines are equipped with means for carrying out valve functions. One such means is a slide system having one circular lower slide (also called the "distributor" or "stator") and one circular upper slide (also called the "runner" or "rotor"). The sweeping and filling of the "stem lamps" is rendered possible in a sequence controlled by the arrangement of passageway openings formed in the upper and lower slides. The upper and lower slide each consists of a steel ring which has a generally planar surface area including the openings of the passageways.
During the sweeping, filling and evacuating of the interior of a glass bulb, corresponding passageways in the upper and lower slides are in communication. To switch over to other passageways, the upper slide rotates on the lower slide. The upper slide may, however, also be rotated continuously, whereby the openings of the passageways in the upper and lower slides will overlap for only a short time.
The engaging surfaces of the upper and lower slides are covered by an oil film to seal the communicating, or for a short time, overlapping openings of the passageways. This also reduces the friction between upper and lower slides.
The stems of the "stem lamps" project into holders, each of which is surrounded by a cylindrical housing, called the "pump connecting piece". The pump connecting piece is connected to passageways in the upper slide, or rotor, which ultimately communicate with the sweeping or filling gas or vacuum sources.
With oil-sealed slides, the oil creating the sealing film can be carried along by the gases, in particular at high speed operation of the sweeping and filling apparatus or during a process called "blowing-out" or "clean-blowing". In addition, there is the danger that oil can accumulate in the connecting passageways. When filling the stem lamps, oil vapors may form which can enter the interior of the lamp bulb along with the gas. In such case, oil is in the closed bulb after the melting-off or sealing-off of the stem. During normal usage, oil inclusions in the lamps heighten the risk of a premature failure of the lamps.
It is an object of this invention to improve an apparatus of the type described above such that no oil can get into the interior of the lamp bulbs.